1. Field of the Invention
This invention relates to the shortening of the closeup focal length of a zoom lens system, particularly, a wide angle zoom lens system.
2. Description of the Prior Art
A zoom lens system covering a wide angle of view, the so-called two-group wide angle zoom lens which comprises two groups, i.e., a first group which is a divergent lens group and a second group which is a convergent lens group, has recently been developed. Various problems which have been unavoidable in conventional wide angle zoom lenses, such as variations in spherical aberration, coma and astigmatism resulting from zooming, particularly, significant negative distortion on the short focal length side, have been solved. Recent years have seen the advent of wide angle zoom lenses having high performance. However, if the diameter of the forward lens is reduced, or if the entire lens system is arranged in a compact form, the aforementioned variations in aberrations cannot always be corrected satisfactorily. Particularly on the long focal length side, spherical aberration becomes considerably over-corrected and if the first group is moved forwardly to effect focusing upon an object which is close, the tendency toward over-correction becomes more pronounced, and results in extreme over-correction of spherical aberration. Therefore, in a wide angle zoom lens system comprising a divergent group and a convergent group, it has been difficult to enhance the image-forming performance of close range objects, and it has been unavoidably necessary to confine the closeup focal length to a relatively long distance.